Usually, a canned motor pump allows a portion of a treating liquid to circulate within a rotor chamber of a canned motor section for cooling the motor section and for lubricating its bearings. In the canned motor pump utilizing a canned motor of H or C type insulation which is poor in heat resistance, however, direct cooling of the canned motor section with a treating liquid is difficult for the hot treating liquid above 200.degree. C. In such case, the motor section is provided at its outer wall with a jacket for water-cooling in order to protect the canned motor section.
Generally, the heat resistance of the conventional motor of C type insulation is limited to 220.degree. C. at highest and thus a temperature of the liquid to be introduced into such canned motor must be controlled about scores of degrees below the limited temperature. For this reason, the conventional canned motor pump for treating the hot liquid above 180.degree. C. is usually of a water-cooling type, as illustrated in FIG. 1.
Namely, the canned motor pump in FIG. 1 comprises a pump section 10 and a motor section 12 thermally separated from each other by anadapter 14 which is provided with a pressure balancing hole 18 for preventing cavitation of an auxiliary impeller 16. Thus, a space pressurized by a main impeller is communicated with a rotor chamber 22 for its pressurization. In this case, small size of the pressure balancing hole 18 allows only a small amount of liquid to flow from the pump section 10 to the motor section 12. In order to cool the motor and to lubricate its bearings, a stator assembly 24 is provided at its outer wall with a heat exchanger 26 to which is circulated the liquid of the motor section 12 by means of the auxiliary impeller 16 provided within the rotor chamber 22. Thus, circulation of the liquid in the motor section 12 is carried out as follows: the liquid pressurized by the auxiliary impeller 16 is introduced through a first circulation tube 28 into an inner pipe 30 of the heat exchanger 26 where the liquid is cooled by a cooling water, and then is introduced through a second circulation tube 32 and a rear bearing housing 34 into the rotor chamber 22 while lubricating a rear bearing 36. Then, the liquid flows through a gap between a stator can 38 of the stator assembly 24 and a rotor can 42 of a rotor assembly 40 for cooling the motor. The liquid, on cooling the motor has its temperature increased a few degrees, lubricates a front bearing 44 and then returns to a suction part of the auxiliary impeller 16, thereby to repeat the circulation. The cooling water introduced into the heat exchanger 26 allows the circulated liquid through the circulation tubes 28, 32 to be cooled and further the motor to be cooled through the outer wall of the stator assembly 24 as a heat transfer surface.
In such type of the conventional canned motor pump a considerable loss of heat, such as exotherm of the motor and heat of the treating liquid, is caused by the cooling water. Further, the heat exchanger and its tubings, as well as accompanying equipments for feeding and discharging the cooling water and for alarming water stoppage may constitute an enormous and complicated apparatus and thus require strict maintenance for preventing corrosion and scaling of the apparatus due to the cooling water, resulting in a considerable increase in an initial investment and a maintenance cost.
In order to solve the problems associated with the conventional canned motor pump as described hereinabove, it is necessary to improve the heat resistance of the canned motor or motor components, and more importantly to increase the dielectric strength of its winding at a high temperature. The conventional canned motor of a general construction may be thermally deteriorated in its winding and insulation at a high temperature above 200.degree. C., thereby to reduce its mechanical strength with consequent damage the insulation.
In view of the foregoing, the applicant has already developed and proposed a canned motor pump having satisfactory dielectric strength at temperatures above 300.degree. C., in which a synthetic fluoro-mica with an organic solvent is suspended in an organosilicon compound solvent for impregnation and curing thereby to form an insulation for windings, in which insulation a fluoro compound vaporized from the fluoro mica is combined with siloxane from the organosilicon compound at the high temperature above 200.degree. C. to form a ceramic-like material for improving the mechanical strength and the dielectric strength of the windings, such as a field winding.
According to such canned motor pump for use in an atmosphere of the high temperature, the canned motor having improved heat resistance is connected to the pump section through an adapter for thermally separating the motor section and a portion of the treating liquid of high temperature is circulated into the canned motor section through an outer tubing for recovering the exotherm of the motor in the liquid, thereby to achieve a lower operation cost as well as savings of resources and energy through the simple construction.
With such type of the canned motor pump for the high temperature, however, the stator assembly of the motor section at its outer circumference is exposed to the atmosphere, so that a portion of generated heat from the motor may be dissipated into the atmosphere through the circumference as a heat transfer surface, resulting in a considerable loss of heat and energy, leading to an economical disadvantage.
It has now been found out that the canned motor pump of a simple construction, which may solve the problems of the conventional canned motor pump and improve the energy saving effect through efficient recovery of the generated heat from the motor, may be achieved by providing a jacket on the outer wall of the motor section, introducing a portion of the treating liquid pressure in the motor section into said jacket for completely absorbing the generated heat of the motor into said portion of the liquid and circulating the liquid to a suction side of the pump section or a lower pressure zone of the pump tubing system.